An incurable cancer of the brain

An incurable cancer of the brain
You have been, but it seems that I was wrong:
There is a cure, though agonizing pain,
I have found it through my own hard and long
Reflection, upon your vicious thug gang
Of friends. The banality of evil,
Never more banal, and the way you hang
Together, like pond scum, each single cell
Incapable of separate existence
But must fester as part of a green mass
Of slow but ever-growing pestilence,
Choking the fresh water of the striped bass:
Air-gulping free-swimmers are well-hated.
Breathing, as we know, is under-rated.